1. Field of the Invention
The present invention relates to a diffusing reflector and method of manufacturing the same reflector and moreover a reflection type display apparatus utilizing the same diffusing reflector.
2. Description of Related Art
A display apparatus utilizing a liquid crystal as an electro-optical layer is formed in the flat-panel shape characterized in thin and light weight structure assuring low power consumption. Therefore, such display apparatus has been developed for wide application field such as a display of hand-held devices. An electro-optical substance such as liquid crystal is not self light generating type and displays an image by selectively transmitting or shielding the external light beam. Such passive type display apparatus can be classified into the transmission type and reflection type depending on the lighting system.
In the transmission type display apparatus, a panel holding liquid crystal, for example, as the electro-optical layer between a couple of transparent substrates is produced and a light source for lighting (backlight) is arranged at the rear surface of the panel and an image can be observed from the front side of panel. In the case of this transmission type, the backlight is essential and a fluorescent lamp, for example, is used as the light source. In the case of considering the display apparatus as a whole, since the backlight consumes the greater part of electrical power, it is not suitable for display of hand-held device. Meanwhile, in the case of the reflection type, a reflector is arrangedat the rear surface of panel, while external light such as the natural light is incident to the front side and an image can also be observed from the front side by utilizing the reflected light thereof. Since the light source for lighting the rear surface is not used different from the transmission type, the reflection type display apparatus consumes less amount of electrical power in comparison with the transmission type and therefore it is suitable for display of a hand-held device.
In the reflection type display apparatus, display is realized by utilizing the incident light from the peripheral environment, it is essential to aim at improvement of brightness by effectively utilizing the incident light. Moreover, it is basically required to realize diffusing reflection of the incident light in the panel in order to realize the white display called as so-called paper white. Therefore, the reflection type display apparatus of the related art comprises in many cases a diffusing reflection layer within the panel. This diffusing reflection layer has the surface including fine unevenness and also has the characteristic approximated to the perfect diffusion in order to show the external appearance of paper white as much as possible. However, it is difficult to conclude that the reflection characteristic is sufficient for practical use and it has been considered a problem of the reflection type display apparatus of the related art to improve the condition of unevenness from the stages of design and process in view of improving the reflection characteristic thereof.
The present invention is provided with the following means for solving the problems of the related art and attaining the objects. Namely, according to the present invention, a diffusing reflector can be produced by the following processes.
In the first process, a resin film having photosensitivity is formed on a substrate. In the next process, the resin film is patterned by the photolithography to provide a gathering of pillar-shaped bodies isolated each other. Subsequently, in the next process, heat treatment is performed to allow gentle deformation of individual pillar-shaped bodies in order to form the layer having uneven surface with the maximum inclination angle under 12xc2x0. As the final process, a metal film is formed on the gently modified uneven layer. It is preferable to include the process in which the gently modified uneven surface layer is coated with resin to ease the maximum inclination angle by burying the flat opening between individual pillar-shaped bodies isolated each other. Preferably, individual pillar-shaped bodies are gently modified by conducting the heat treatment at the temperature of about 220xc2x0 C. Preferably, the resin film is divided by the patterning through the photolithography to provide a gathering of polygonal pillar-shaped bodies isolated each other. It is also preferable that the resin film is divided by the patterning so that the size of gap between polygonal pillar-shaped bodies isolated each other becomes almost equal to the minimum resolution of the photolithography.
The present invention includes a structure itself of the diffusing reflector. Namely, the diffusing reflector of the present invention is composed of a resin film forming the heaping areas and a metal film formed on the surface of such heaping areas. Namely, the present invention is characterized in that the heaping areas in which the maximum inclination angle is controlled under 12xc2x0 are formed through reflow of the resin film composed of gathering of pillar-shaped bodies patterned each other previously leaving the opening between such pillar-shaped bodies.
The diffusing reflector produced by the method explained above can be comprised within the reflection type display apparatus. In this case, the reflection type display apparatus is provided, as the basic structure, with a first transparent substrate arranged in the incident side, a second substrate joined with the first substrate via the predetermined gap and is arranged in the opposite side, an electro-optical layer located in the first substrate side within the gap, a diffusing reflection layer located in the second substrate side within the gap and an electrode for impressing a voltage to the electro-optical layer formed in at least one substrate among the first and second substrates. The diffusing reflection layer is composed of a resin film forming the heaping areas and a metal film formed on the heaping areas. As the characteristic of such reflection type display apparatus, the heaping areas in which the maximum inclination angle is controlled under 12xc2x0 is formed by reflow of the resin film consisting of gathering of pillar-shaped bodies divided through the patterning keeping the predetermined opening between pillar-shaped bodies. Preferably, the gentle heaping areas are formed by reflow of resin film consisting of gathering of the pillar-shaped bodies and then burying the opening with the other resin film. It is preferable that the opening left after the reflow of the resin film consisting of gathering of pillar-shaped bodies is buried with the other resin to form the uneven surface having the gentle rolling. In the preferred embodiment of the reflection type display apparatus having such structure, a polarizing plate is arranged in the first substrate side and the liquid crystal layer which functions as the (xc2xc)-wavelength plate depending on the voltage impressing condition is used as the electro-optical layer. In this case, the (xc2xc)-wavelength plate is arranged between the polarizing plate and liquid crystal layer and the liquid crystal layer is composed of the nematic liquid crystal layer having positive dielectric anisotropy and the twisted alignment. This liquid crystal layer functions as the (xc2xc)-wavelength plate when a voltage is not applied and also loses the function of the (xc2xc)-wavelength plate when a voltage is applied.
According to the present invention, in view of improving the reflection characteristic of a diffusing reflector, the inclination angle of the layer having uneven surface is optimized. Namely, the reflection characteristic of the diffusing reflector can be improved by controlling the maximum inclination angle to 12xc2x0 or under. In general, when the maximum inclination angle becomes larger, angular distribution of reflected light beam is widened. When the maximum inclination angle is under 12xc2x0 and particularly located near 10xc2x0, the diagonally incident external light increases in the element to be reflected to an observer located at the front side of apparatus. Therefore, it has been proved that bright image can be obtained. When the maximum inclination angle becomes larger than 12xc2x0, the element of reflected light totally reflected in the panel increases. Therefore such maximum inclination angle is not preferable.